This invention is directed to an open sea skimming barge for the removal of crude oil, refined hydrocarbon product or other floating pollutant slicks from water surfaces, particularly those slicks caused by accidents while handling, transporting, processing, controlling, producing or exploring for hydrocarbons.
For many years, crude oil and refined hydrocarbon product spillages at sea have been a problem. The environmental damage and cleanup costs of large spills can reach millions of dollars, which along with damaging publicity present a serious problem for the industries involved. As more crude oil and refined hydrocarbon products are being transported over longer distances by larger tankers, and with the increases in offshore hydrocarbon exploration and production, the problem of dealing with spillages is likely to increase.
Since crude oil and refined hydrocarbon product spillages are likely to continue at an ever increasing rate, a method and apparatus are needed for reliably removing the spillages as rapidly as possible from the surface of the water in open seas, or large bays, lakes and rivers.
Slicks in the open sea vary considerably in their characteristics depending upon the type of crude oil or refined hydrocarbon product spilled, the weather, size of the spillage and the condition of the sea. The slick thickness may vary on the surface of the sea and be considered as having a portion extending below the surface of the sea due to the continual degradation of the slick by the elements and natural evaporation of the hydrocarbons.
When compared with the problems of recovering spillages in quiet, calm seas, bays, harbors or rivers, the recovery of spillages in the open sea, particularly under adverse weather conditions, is clearly more difficult. Open sea spillage recovery requires equipment which must be self-contained, capable of maintaining its station over long periods of time, and capable of operating in adverse weather conditions, such as in seas of eight feet or more. Frequently in the past, many types of spillage recovery equipment have only been effective in relatively calm conditions and were intended for short term operation.
To date, many types of methods and apparatus have been used in attempts to deal with spillages.
Detergents and other chemical treatments of slicks have been, and continue to be utilized, but each has limitations and inherent hazards which can be as undesirable as the slicks themselves.
Early attempts were usually directed to dealing with spillages of oil in flowing streams. Typical apparatus comprised collection reservoirs or rotating drum type pumps, such as shown in U.S. Pat. Nos. 48,411; 54,014 and 95,089.
Prior spillage removal equipment employing endless belt transports, such as those described in U.S. Pat. Nos. 3,314,540 and 3,314,545, are considered by their design to have a limited capacity to collect floatage of both solid and liquid forms of the spillage. More particularly, some prior constructions depend on the adherence of floatage to the belt transport to recover solid and liquid floating material of the spillage. Others provide structures that push the spillage to recover the same, and still others require pumps to enhance the collection of floatage, such as the belt transport sold by Marco Pollution Control, Seattle, Wash. Yet others tend at least to partially bulldoze the spillage being recovered, which increases the likelihood that some spillage will be pushed to the side and hence not collected.
Another prior skimming type spillage recovery equipment utilizes a submerged forward lip or ledge and processes all the inflow, whether floatage to be removed or the liquid spillage being skimmed, which is above the shelf edge. This type of recovery equipment generally takes in the floatage and liquid spillage which is above the shelf edge, and hence leaves floatage and liquid spillage uncollected where there is a considerable depth thereof. This type of arrangement is illustrated in U.S. Pat. Nos. 3,690,464; 3,875,062 and 3,823,828. This skimming equipment illustrated utilizes the forward velocity of the vessel and the pumping or suction action of either the vessel's propulsion means or a separate pumping means to help enhance the flow of spillage over the submerged forward lip. Wave action will affect this type of skimming equipment since heavy seas will cause the excessive inflow of water with the spillage since the control of the depth of the forward lip below the surface of the water is difficult. With the excessive inflow of water with the spillage, it will also become more difficult to subsequently separate the spillage therefrom, thereby requiring other types of separation equipment or much larger on-board holding tanks for the excessive water and spillage.
Yet another prior skimming type spillage recovery equipment utilizes a downwardly inclined member having a horizontal slot or opening at the lower end thereof to force the slick downwardly during the passage of the inclined member thereover and into the slot or opening due to the pressure differential created by the buoyancy of the slick. The pressure differential may be increased to ensure the slick will flow into the slot or opening through the use of pumps to decrease the pressure within the cavity fed by the slot or opening. Typical examples of this type of equipment are described in U.S. Pat. Nos. 3,465,882; 3,615,017; 3,715,034; 3,860,519 and 3,966,615 and published U.K. patent application No. GB 2,005,554. In this type of skimming equipment the skimmer may be stationary having a flowing body of water moving thereby, as in U.S. Pat. No. 3,465,882, may be self-propelled through the water utilizing a reduced collection tank pressure, as in U.S. Pat. No. 3,615,017, may be self-propelled utilizing a variable flap to control the slot or opening width and merely utilize a gravity settling technique in the collection tank, as in U.S. Pat. No. 3,715,034, or may be self-propelled utilizing a reduced collection tank pressure and a wave-receiving splash plate on the bow thereof, as in published U.K. patent application No. GB 2,005,554. This type of spillage recovery equipment requires relatively high velocities downwardly along the inclined member of the spillage relative to the inclined member, i.e., for example, five to ten knots, for most efficient operation and also has a tendency to sidewardly deflect a portion of the spillage, even with the addition of vertical extensions along the inclined member to prevent the same. As with the submerged forward lip type skimming equipment, this type of equipment suffers performance degradation in heavy seas since it is difficult to control the height of the inclined member with respect to the wave height. Also, since in open sea skimming operations high forward velocities are required to maintain the high velocities of the spillage downwardly along the inclined member with respect to the inclined member, sideward deflection of the slick, splashing of the slick over the bow of the vessel, and large bow waves created by pushing and churning of the spillage, even in calm seas let along heavy seas, are problems.
Still another type of spillage recovery equipment utilizes a rotating downwardly inclined endless belt to force the slick downwardly during the passage of the belt thereover and into a collection tank due to the pressure differential created by the buoyancy of the slick as it is depressed. Such equipment is illustrated in U.S. Pat. Nos. 3,314,540; 3,804,251; and 3,812,968. While not necessarily requiring high forward velocities for skimming operations, such velocities can be artificially created by increasing the rotational speed of the belts. For open sea skimming operations this type of equipment may require the use of many rotating endless belt assemblies, may have problems operating in heavy seas due to the inability to compensate for wave height variation thereby having waves break over the vessel on which the equipment is installed, and may sidewardly deflect portions of the slick during operations thereby lowering the effective skimming efficiency of the device.
Other types of recovery equipment utilize a combination of slick separation techniques in order to remove as much water from the spillage in order to reduce handling and storage problems on board the equipment. One such device having an initial submerged forward lip to skim the slick, a plurality of rotating drums to further separate the water from the slick and a gravity settling processing tank to further separate the water from the slick is illustrated in U.S. Pat. No. 3,700,107. Another such device having an initial suction type skimming device, a further gravity settling tank for a secondary water and slick separation means and finally a centrifugal type separating means is illustrated in U.S. Pat. No. 3,957,646.